A chemical compound that helps control the pH of a solution by adding or removing hydrogen ions is called a buffer.

Here's why:

* pH: A measure of the acidity or alkalinity of a solution. A lower pH indicates a more acidic solution, while a higher pH indicates a more alkaline (basic) solution.

* Hydrogen ions (H+): These ions are responsible for the acidity of a solution. The more H+ ions present, the lower the pH.

* Buffers: These are solutions that resist changes in pH when small amounts of acid or base are added. They do this by either donating H+ ions (if the pH rises) or absorbing H+ ions (if the pH drops).

Examples of buffers:

* Bicarbonate buffer: Found in blood, this buffer helps maintain the blood's pH at a slightly alkaline level.

* Phosphate buffer: Plays a role in regulating pH within cells.

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